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Abstract:

Methods and systems are provided for producing a fuel from a renewable
feedstock. The method includes deoxygenating the renewable feedstock in a
deoxygenation zone to produce hydrocarbons with normal paraffins. The
hydrocarbons with normal paraffins are isomerized to produce hydrocarbons
with branched paraffins. The hydrocarbons with branched paraffins are
fractionated to produce a naphtha at a naphtha outlet, where the naphtha
is further isomerized.

Claims:

1. A method of producing fuel from a renewable feedstock, the method
comprising the steps of: deoxygenating the renewable feedstock in a
deoxygenation reaction zone to produce hydrocarbons comprising normal
paraffins; isomerizing the hydrocarbons comprising normal paraffins to
produce hydrocarbons comprising branched paraffins; fractionating the
hydrocarbons comprising branched paraffins to produce a naphtha at a
naphtha outlet; and isomerizing the naphtha from the naphtha outlet.

2. The method of claim 1 wherein isomerizing the hydrocarbons comprising
normal paraffins further comprise isomerizing the hydrocarbons comprising
normal paraffins in a first isomerization reaction zone at isomerization
conditions; and wherein isomerizing the naphtha further comprises
isomerizing the naphtha in the first isomerization reaction zone.

3. The method of claim 2 wherein isomerizing the naphtha further
comprises adding the naphtha to the first isomerization reaction zone
such that the naphtha bypasses a portion of an isomerization catalyst
positioned within the first isomerization reaction zone.

4. The method of claim 2 wherein isomerizing the naphtha further
comprises isomerizing the naphtha in a second isomerization reaction
zone.

5. The method of claim 1 wherein isomerizing the naphtha further
comprises isomerizing the naphtha in a second isomerization reaction
zone.

7. The method of claim 1 wherein deoxygenating the renewable feedstock
further comprises deoxygenating the renewable feedstock wherein the
renewable feedstock comprises oil extracted from a plant or an animal.

8. The method of claim 1 further comprising sulfiding a deoxygenation
catalyst in the deoxygenation reaction zone.

9. The method of claim 1 further comprising: contacting the renewable
feedstock with a guard bed catalyst at pretreatment conditions.

10. The method of claim 1 further comprising: pre-cleaning the renewable
feedstock in a pre-cleaning zone.

11. A method of producing fuel from a renewable feedstock, the method
comprising the steps of: contacting the renewable feedstock with a
deoxygenation catalyst to produce hydrocarbons comprising normal
paraffins; contacting the hydrocarbons comprising normal paraffins with
an isomerization catalyst to produce hydrocarbons comprising branched
paraffins; fractionating the hydrocarbons comprising branched paraffins
to produce a naphtha at a naphtha outlet; and isomerizing the naphtha
from the naphtha outlet.

12. The method of claim 11 wherein contacting the hydrocarbons comprising
normal paraffins with the isomerization catalyst further comprises
contacting the hydrocarbons comprising normal paraffins with the
isomerization catalyst wherein the isomerization catalyst is within a
first isomerization reaction zone; and wherein isomerizing the naphtha
further comprises contacting the naphtha with the isomerization catalyst
in the first isomerization reaction zone.

13. The method of claim 12 wherein isomerizing the naphtha further
comprises adding the naphtha to an isomerization reactor at a side inlet
of the isomerization reactor, wherein the isomerization catalyst is
positioned within the isomerization reactor and wherein the side inlet is
positioned such that the naphtha bypasses some of the isomerization
catalyst within the isomerization reactor.

14. The method of claim 12 wherein isomerizing the naphtha further
comprises contacting the naphtha with the isomerization catalyst in a
second isomerization reaction zone.

15. The method of claim 11 wherein contacting the hydrocarbons comprising
normal paraffins with the isomerization catalyst further comprises
contacting the hydrocarbons comprising normal paraffins with the
isomerization catalyst wherein the isomerization catalyst is within a
first isomerization reaction zone; and wherein isomerizing the naphtha
further comprises isomerizing the naphtha in a second isomerization
reaction zone different than the first isomerization reaction zone.

16. The method of claim 11 wherein contacting the renewable feedstock
with the deoxygenation catalyst further comprises contacting the
renewable feedstock with the deoxygenation catalyst wherein the renewable
feedstock comprises glycerides or free fatty acids.

17. The method of claim 11 wherein contacting the renewable feedstock
with the deoxygenation catalyst further comprises contacting the
renewable feedstock with the deoxygenation catalyst wherein the renewable
feedstock comprises oil extracted from a plant or an animal.

18. The method of claim 11 further comprising sulfiding the deoxygenation
catalyst.

19. The method of claim 1 further comprising: pre-cleaning the renewable
feedstock in a pre-cleaning zone.

20. A system for producing fuel from a renewable feedstock comprising; a
renewable feedstock feed system; a deoxygenation reaction zone coupled to
the renewable feedstock feed system; a first isomerization reaction zone
coupled to the deoxygenation reaction zone; a fractionation zone coupled
to the first isomerization reaction zone, wherein the fractionation zone
comprises a naphtha outlet; and an isomerization reactor, wherein the
naphtha outlet is coupled to the isomerization reactor.

Description:

TECHNICAL FIELD

[0001] The present disclosure generally relates to systems and methods for
producing fuels from renewable feedstocks, and more particularly relates
to systems and methods for converting renewable feedstocks into branched
paraffins useful as fuel.

BACKGROUND

[0002] Many existing processes for converting renewable feedstocks into
diesel fuels or jet fuels produce a naphtha stream as a co-product. The
naphtha stream often includes many normal paraffin compounds, which are
straight chain paraffins, that have a relatively low octane value. The
octane value can be increased by isomerizing the normal paraffins into
branched paraffins, because branched paraffins produce higher octane
values. Increasing the octane value of the naphtha stream increases the
value of the naphtha stream, and a more valuable naphtha stream increases
the value of the overall process for converting renewable feedstocks into
fuel.

[0003] Accordingly, it is desirable to develop methods and systems for
increasing the degree of isomerization of naphtha produced as a
co-product with other fuels from renewable feedstocks. In addition, it is
desirable to develop methods and systems for increasing the octane value
of naphtha produced from renewable feedstocks. Furthermore, other
desirable features and characteristics of the present embodiment will
become apparent from the subsequent detailed description and the appended
claims, taken in conjunction with the accompanying drawings and this
background.

BRIEF SUMMARY

[0004] A method is provided for producing fuel from renewable feedstocks.
The renewable feedstock is deoxygenated in a deoxygenation zone to
produce hydrocarbons with normal paraffins. The hydrocarbons with normal
paraffins are isomerized to produce hydrocarbons with branched paraffins.
The hydrocarbons with branched paraffins are fractionated to produce a
naphtha at a naphtha outlet, where the naphtha is further isomerized.

[0005] Another method is provided for producing a fuel from a renewable
feedstock. The renewable feedstock is contacted with a deoxygenation
catalyst to produce hydrocarbons with normal paraffins. The hydrocarbons
with normal paraffins are contacted with an isomerization catalyst to
produce hydrocarbons with branched paraffins. The hydrocarbons with
branched paraffins are fractionated to produce a naphtha at a naphtha
outlet, and the naphtha is then isomerized.

[0006] A system is also provided for producing a fuel from a renewable
feedstock. The system includes a renewable feedstock feed system coupled
to a deoxygenation reaction zone. A first isomerization reaction zone is
coupled to the deoxygenation reaction zone, and a fractionation zone is
coupled to the first isomerization reaction zone. The fractionation zone
includes a naphtha outlet, and the naphtha outlet is coupled to an
isomerization reactor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Various embodiments will hereinafter be described in conjunction
with the following figures, wherein like numerals denote like elements,
and wherein:

[0008] FIG. 1 is a schematic diagram of an exemplary embodiment of a
system and method for producing fuel from a renewable feedstock; and

[0009] FIG. 2 is a schematic diagram illustrating an exemplary embodiment
of a system and method for fractionating and isomerizing fuel products
produced from a renewable feedstock.

DETAILED DESCRIPTION

[0010] The following detailed description is merely exemplary in nature
and is not intended to limit the application or uses of the embodiment
described. Furthermore, there is no intention to be bound by any theory
presented in the preceding technical field, background, brief summary, or
the following detailed description.

[0011] Various processes for converting renewable feedstocks into fuels,
especially into diesel fuel or jet fuel, also produce a naphtha
co-product. The naphtha co-product is primarily hydrocarbon molecules
with 5 to 8 carbon atoms and boils at a lower temperature than diesel or
jet fuel. The naphtha co-product could be used for gasoline or other
fuels, but it has a significant component of straight chain (normal)
paraffins that have a low octane value. The octane value of the naphtha
is increased by isomerizing the normal paraffins to produce branched
paraffins, and the higher octane value increases the monetary value of
the naphtha co-product.

[0012] Reference is now made to the exemplary embodiment illustrated in
FIG. 1. A renewable feedstock 10 is processed to produce various types of
fuel, such as diesel fuel, jet fuel, gasoline, liquid propane gas (LPG),
etc. The term renewable feedstock 10 is meant to include feedstocks other
than those derived from petroleum crude oil, and includes oils extracted
from plants or animals. The renewable feedstocks 10 as contemplated
herein are any of those which include glycerides or free fatty acids
(FFA). Most of the glycerides will be triglycerides, but monoglycerides
and diglycerides may be present and processed as well. Examples of these
renewable feedstocks 10 include, but are not limited to, canola oil, corn
oil, rapeseed oil, soybean oil, colza oil, tall oil, sunflower oil,
hempseed oil, olive oil, linseed oil, coconut oil, castor oil, peanut
oil, palm oil, mustard oil, camelina oil, pennycress oil, tallow, yellow
and brown greases, lard, train oil, jatropha oil, fats in milk, fish oil,
algal oil, sewage sludge, and the like. Additional examples of renewable
feedstocks 10 include non-edible vegetable oils, such as oils from
Madhuca indica (mahua), Pongamia pinnata, and Azadirachta indica (neem).

[0013] The glycerides and FFAs of the typical vegetable or animal fat
contain aliphatic hydrocarbon chains in their structure which have about
8 to about 24 carbon atoms. The majority of the fats and oils contain
high concentrations of fatty acids with 16 to 18 carbon atoms, and many
types of oils contain aliphatic hydrocarbon chains within a limited
range, such as 14 to 18. Only a limited number of oil types include
aliphatic hydrocarbon chains covering the entire range from about 8
carbon atoms to about 24 carbon atoms, so the 8 to 24 carbon atoms range
is meant to encompass mixtures of all types of oils. Co-feeds, or
mixtures of renewable feedstocks 10 and petroleum derived hydrocarbons,
may also be used as the feedstock. Other feedstock components that may be
used, especially as a co-feed component in combination with the above
listed feedstocks, include spent motor oils and industrial lubricants;
used paraffin waxes; liquid derived from the gasification of coal,
biomass, or natural gas followed by a downstream liquefaction step such
as Fischer-Tropsch technology; liquids derived from depolymerization
(thermal or chemical) of waste plastics such as polypropylene, high
density polyethylene, and low density polyethylene; and other synthetic
oils generated as byproducts from petrochemical and chemical processes.
Mixtures of the above feedstocks may also be used as co-feed components.
One advantage of using a co-feed component is the transformation of what
may have been a waste product into a valuable co-feed component to the
current process.

[0014] The renewable feedstock 10 is stored and delivered for processing
by a renewable feedstock feed system 12. In an exemplary embodiment, the
renewable feedstock feed system 12 includes a renewable feedstock storage
tank 14, renewable feedstock pump 16, and associated piping. The
renewable feedstock feed system 12 delivers a renewable feedstock feed
stream 18 for further processing. Other embodiments of the renewable
feedstock feed system 12 exist, such as a pipeline from a different
source, and a pressurized renewable feedstock storage tank 14 without a
renewable feedstock pump 16.

[0015] Many renewable feedstocks 10 that can be used herein contain a
variety of impurities. For example, tall oil is a byproduct of the wood
processing industry, and includes esters and rosin acids in addition to
FFAs. Rosin acids are cyclic carboxylic acids. The renewable feedstocks
10 may also contain contaminants such as alkali metals, (e.g. sodium and
potassium), phosphorous, various solids, water, and detergents. In some
embodiments, the renewable feedstock 10 is pre-cleaned in an optional
pre-cleaning zone 20 to improve downstream processing operations, and
several different types of pre-cleaning are possible. For example, the
pre-cleaning zone 20 may be configured to provide a mild acid wash by
contact with dilute sulfuric, nitric, citric, phosphoric, or hydrochloric
acid in a reactor. The acid wash can be a continuous process or a batch
process, and the dilute acid contact can be at ambient temperature and
atmospheric pressure. Other possible pre-cleaning steps include, but are
not limited to, contacting the renewable feedstock 10 with an ion
exchange resin such as Amberlyst®-15, subjecting the renewable
feedstock 10 to a caustic treatment, bleaching the renewable feedstock 10
with an adsorbent, filtration, solvent extraction, hydro processing, or
combinations of the above.

[0016] In some embodiments, a sulfiding agent 22 is added to the renewable
feedstock 10. Several reactors described more fully below use catalysts
of various types, and one or more of these catalysts can be used in a
sulfided state in various embodiments. Sulfur is added to the process to
maintain the catalysts in the sulfided state. The sulfiding agent 22 is
added at a sulfiding agent inlet 24. The sulfur is measured as elemental
sulfur, regardless of the compound containing the sulfur, and can be
added in many forms. For example, suitable sulfiding agents 22 include,
but are not limited to, dimethyl disulfide, dibutyl disulfide, and
hydrogen sulfide. The sulfur may be obtained from various sources, such
as part of a hydrogen stream from a hydrocracking unit or hydro treating
unit, or sulfur compounds removed from kerosene or diesel, and disulfide
oils removed from sweetening units such as Merox® units. A
deoxygenation catalyst is described more fully below, and sulfur
concentrations of less than 2,000 ppm are typically sufficient to
maintain the deoxygenation catalyst and the other catalysts described
below in a sulfided state. FIG. 1 illustrates adding the sulfiding agent
22 to the renewable feedstock feed stream 18, but other embodiments are
possible. For example, some renewable feedstocks 10 contain sufficient
sulfur to maintain the catalysts in a sulfided state. Sulfur can also be
added to the renewable feedstock storage tank 14, the reactors containing
the catalysts, or other locations.

[0017] In an exemplary embodiment, a recycle hydrogen stream 80 (described
more fully below) is added to the renewable feedstock feed stream 18 and
flows downstream to a guard bed 26. A portion of a hot separator bottoms
stream 50 (described more fully below) is also added to the renewable
feedstock feed stream 18 before entry into the guard bed 26. The guard
bed 26 removes metals from the renewable feedstock 10 by contacting the
renewable feedstock feed stream 18 with a guard bed catalyst 28 at
pretreatment conditions. The guard bed catalyst 28 may initiate a
deoxygenation reaction of the renewable feedstock feed stream 18 to some
degree, as described more fully below. In some embodiments, the guard bed
catalyst 28 is alumina, either with or without demetallation catalysts
such as nickel or cobalt, but other guard bed catalysts 28 are also
possible. The guard bed 26 is operated at a temperature from about
40° C. to about 400° C., for example from about 150°
C. to about 300° C. Operating pressures for the guard bed 26 are
from about 690 kilopascals (kPa) absolute (100 pounds per square inch
absolute (psia)) to about 13,800 kPa absolute (2,000 psia), for example
from about 1,380 kPa absolute (200 psia) to about 6,900 kPa absolute
(1,000 psia). A portion of the hot separator bottoms stream 50 may be
added at various locations in the guard bed 26 to aid in temperature
control, hydrogen solubility, or other purposes, but in other embodiments
different streams or no streams are added at side locations in the guard
bed 26.

[0018] After the optional guard bed 26, a guard bed effluent 30 flows
downstream to a deoxygenation reaction zone 40 including one or more
catalyst beds in one or more reactors. In the deoxygenation reaction zone
40, the guard bed effluent 30 is contacted with a deoxygenation catalyst
42 (sometimes referred to as a hydrotreating catalyst) in the presence of
hydrogen at deoxygenation conditions. The hydrogen for this reaction is
provided from the recycle hydrogen stream 80 added to the renewable
feedstock feed stream 18. Under these conditions, the olefinic or
unsaturated portions of n-paraffinic chains are hydrogenated.
Additionally, any deoxygenation reactions that did not take place in the
guard bed 26 are completed in the deoxygenation reaction zone 40. In some
embodiments, a portion of the hot separator bottoms stream 50 is added at
various locations in the deoxygenation reaction zone 40 to aid in
temperature control, hydrogen solubility, and other purposes. In other
embodiments, streams other than the hot separator bottoms stream 50 (or
even no streams) are added at side locations in the deoxygenation
reaction zone 40. A deoxygenation effluent 44 exits the deoxygenation
reaction zone 40.

[0019] Deoxygenation catalysts 42 are any of those well known in the art,
such as nickel, nickel/molybdenum, or cobalt/molybdenum dispersed on a
high surface area support. Other deoxygenation catalysts 42 include one
or more noble metal catalytic elements dispersed on a high surface area
support. Non-limiting examples of noble metals include platinum (Pt)
and/or palladium (Pd). Deoxygenation conditions include a temperature of
about 40 degrees centigrade (° C.) to about 400° C., and a
pressure of about 690 kilopascals (kPa) absolute (100 psia) to about
13,800 kPa absolute (2,000 psia). In another embodiment the deoxygenation
conditions include a temperature of about 200° C. to about
300° C., and a pressure of about 1,380 kPa absolute (200 psia) to
about 6,900 kPa absolute (1,000 psia). Other operating conditions for the
deoxygenation reaction zone 40 can also be used. A sulfiding agent 22,
such as from the sulfiding agent inlet 24 or from the renewable feedstock
10, maintains the deoxygenation catalyst 42 in a sulfided state.

[0020] The deoxygenation catalysts 42 discussed above are also capable of
catalyzing decarboxylation, decarbonylation and/or hydrodeoxygenation of
the renewable feedstock 10 to remove oxygen. Decarboxylation,
decarbonylation, and hydrodeoxygenation are herein collectively referred
to as "deoxygenation reactions", and the deoxygenation reactions and the
olefin hydrogenation reactions simultaneously occur in the deoxygenation
reaction zone 40. Deoxygenation conditions include a relatively low
pressure of about 3,450 kPa (500 psia) to about 6,900 kPa (1,000 psia), a
temperature of about 200° C. to about 400° C., and a liquid
hourly space velocity of about 0.2 to about 10 hr-1. In another
embodiment the deoxygenation conditions include the same relatively low
pressure of about 3,450 kPa (500 psia) to about 6,900 kPa (1,000 psia), a
temperature of about 290° C. to about 350° C., and a liquid
hourly space velocity of about 1 to about 4 hr-1.

[0021] Deoxygenation is an exothermic reaction, so the temperature in the
deoxygenation reaction zone 40 increases as the hydrocarbons from the
renewable feedstock 10 pass through. Decarboxylation and
hydrodeoxygenation reactions begin to occur as the temperature increases.
The rate of the deoxygenation reactions increases from the front of the
bed to the back of the bed as the temperature increases. The
deoxygenation reaction zone 40 can include one or more reactors in
series, and can also include parallel reactors or sets of reactors.

[0022] The hydrodeoxygenation reaction consumes hydrogen and produces
water as a byproduct, while the decarbonylation and decarboxylation
reactions produce carbon monoxide (CO) or carbon dioxide (CO2)
without consuming hydrogen. However, hydrogen is present for all the
reactions in the deoxygenation reaction zone 40, regardless of whether
the reaction consumes hydrogen or not. The product from the deoxygenation
reactions includes a liquid portion and a gaseous portion. The liquid
portion present in the deoxygenation effluent 44 includes hydrocarbon
compounds that are largely normal paraffin compounds (n-paraffins) having
a high cetane number. The gaseous portion includes hydrogen, carbon
dioxide (CO2), carbon monoxide (CO), water vapor, propane, and
perhaps sulfur components such as hydrogen sulfide. It is possible to
separate and collect the liquid portion (the hydrocarbons including
n-paraffins) as a diesel fuel product without further reactions. However,
in most climates, at least a portion of the liquid n-paraffins can be
isomerized to produce branched paraffins, which improves the cold flow
properties of the fuel.

[0023] In an exemplary embodiment, the deoxygenation effluent 44 passes to
an optional hot separator 46 downstream from the deoxygenation reaction
zone 40. One purpose of the hot separator 46 is to separate at least some
of the gaseous portion from the liquid portion of the deoxygenation
effluent 44. Much of the gaseous portion, including the recovered
hydrogen, exits the hot separator 46 in a hot separator overhead stream
48, and the liquid portion exits the hot separator in a hot separator
bottoms stream 50. The separated hydrogen is recycled back to the
deoxygenation reaction zone 40 in some embodiments, as described more
fully below. The liquid hydrocarbons including the n-paraffins exit the
hot separator 46 in the hot separator bottoms stream 50.

[0024] In some embodiments, water, CO, CO2, and any ammonia or
hydrogen sulfide are stripped in the hot separator 46 using hydrogen. In
some embodiments (not shown), additional hydrogen is used as the
stripping gas, but other gases could also be used. The temperature is
controlled to achieve the desired separation, and the pressure can be
maintained at approximately the same pressure as the deoxygenation
reaction zone 40 and the isomerization reaction zone (described below) to
minimize both investment and operation costs. Energy is required to
change the temperature or pressure, which increases operating costs, and
additional equipment is needed to enable the process to change the
temperature of pressure, which increases the investment cost. The hot
separator 46 may be operated at conditions ranging from a pressure of
about 690 kPa absolute (100 psia) to about 13,800 kPa absolute (2,000
psia), and a temperature of about 40° C. to about 350° C.
In another embodiment, the hot separator 46 may be operated at conditions
ranging from a pressure of about 1,380 kPa absolute (200 psia) to about
6,900 kPa absolute (1,000 psia), or about 2,410 kPa absolute (350 psia)
to about 4,880 kPa absolute (650 psia), and a temperature of about
50° C. to about 350° C.

[0025] The paraffinic components of the hot separator bottoms stream 50
are primarily n-paraffins which range from about 8 to about 24 carbon
atoms depending on the type of renewable feedstock 10 used. Different
renewable feedstocks 10 will result in different distributions of
paraffins. The hot separator bottoms stream 50 is divided and transferred
to various locations in different embodiments. A portion of the hot
separator bottoms stream 50 may be recycled and added to the guard bed 26
at various locations, and to the deoxygenation reaction zone 40 at
various locations, as described above. In alternate embodiments, other
streams or no streams are recycled in place of the hot separator bottoms
stream 50.

[0026] In an exemplary embodiment, the hot separator bottoms stream 50
also flows to an enhanced hot separator 52 to further separate the
gaseous and liquid components of the deoxygenation effluent 44.
Additional gases are removed from the liquid hydrocarbons with the
n-paraffins, and the gases are vented in an enhanced hot separator
overhead stream 54, which is combined with the hot separator overhead
stream 48. The enhanced hot separator 52 operates at similar conditions
as the hot separator 46. The enhanced hot separator operating conditions
range from a pressure of about 690 kPa absolute (100 psia) to about
13,800 kPa absolute (2,000 psia), and a temperature of about 40°
C. to about 350° C. In another embodiment, the enhanced hot
separator 52 may be operated at conditions ranging from a pressure of
about 1,380 kPa absolute (200 psia) to about 6,900 kPa absolute (1,000
psia), or about 2,410 kPa absolute (350 psia) to about 4,880 kPa absolute
(650 psia), and a temperature of about 50° C. to about 350°
C.

[0027] An enhanced hot separator bottoms stream 56 flows from the enhanced
hot separator 52 downstream to a first isomerization reaction zone 60.
The enhanced hot separator bottoms stream 56 is primarily made up of the
liquid hydrocarbons, including the n-paraffins, from the deoxygenation
reaction zone 40. Fresh hydrogen is added to the enhanced hot separator
bottoms stream 56 from a hydrogen feed line 36, so additional hydrogen is
fed to the first isomerization reaction zone 60. In other embodiments,
the hydrogen could be fed to the first isomerization reaction zone 60 in
other manners, such as from a feed line piped directly into a reactor in
the first isomerization reaction zone 60.

[0028] Isomerization can be carried out in a separate bed of the same
reactor used in the deoxygenation reaction zone 40, or the isomerization
can be carried out in a separate isomerization reactor 58. For ease of
description, the following will address the embodiments where a separate
reaction zone is employed for the first isomerization reaction zone 60.
In an exemplary embodiment, the first isomerization reaction zone 60
includes an isomerization catalyst 62 positioned within an isomerization
reactor 58, and is operated at isomerization conditions. The hydrocarbons
with the n-paraffins in the enhanced hot separator bottoms stream 56 are
contacted with the isomerization catalyst 62 in the presence of hydrogen
to convert at least some of the n-paraffins into branched paraffins. Only
minimal branching is required to overcome the poor cold-flow
characteristics of the n-paraffins used in diesel or jet fuel. In some
embodiments, the predominant isomerized paraffin product is a
mono-branched hydrocarbon, because process conditions that produce
significant branching also increase the risk of excessive cracking that
reduces the yield of diesel or jet fuel. The hydrocarbons used in diesel
and jet fuel generally have more carbons than the hydrocarbons used in
gasoline, on average, and have a higher average boiling point. Besides
improving the cold flow properties of diesel fuel, branched paraffins
also increase the octane rating of gasoline fuels.

[0029] An isomerization effluent 64, which exits the first isomerization
reaction zone 60, is a hydrocarbon stream rich in branched paraffins. By
the term "rich" it is meant that the isomerization effluent 64 has a
greater concentration of branched paraffins than the stream entering the
first isomerization reaction zone 60, and in some embodiments includes
greater than 50 mass percent branched paraffins. The isomerization
effluent 64 may contain 70, 80, or 90 mass percent branched paraffins in
some embodiments, but lower concentrations of branched paraffins are
present in other embodiments. The degree of isomerization can be changed
by adjusting the isomerization conditions. For example, a lower reactor
temperature will decrease the degree of isomerization, and also decrease
the degree of cracking in the first isomerization reaction zone 60.

[0030] The isomerization of the n-paraffins can be accomplished by using a
variety of suitable catalysts. The first isomerization reaction zone 60
includes one or more beds of isomerization catalyst 62, and the catalyst
beds can be in series and/or parallel. A single isomerization reactor 58
may include one or more catalyst beds, so the first isomerization
reaction zone 60 can also include one or more isomerization reactors 58.
In some embodiments, the first isomerization reaction zone 60 is operated
in a co-current mode of operation. Fixed bed trickle down flow or fixed
bed liquid upward flow modes are both suitable. In some embodiments, the
isomerization catalyst 62 is not sulfided, so no sulfiding agents are
added to streams entering the first isomerization reaction zone 60
downstream from the deoxygenation reaction zone 40. In alternate
embodiments, the isomerization catalyst is sulfided.

[0031] Suitable isomerization catalysts 62 include a metal of Group VIII
(IUPAC 8-10) of the Periodic Table and a support material. Suitable Group
VIII metals include platinum and palladium, each of which may be used
alone or in combination. The support material may be amorphous or
crystalline, and many different support materials can be used. Suitable
support materials include, but are not limited to, amorphous alumina,
amorphous silica-alumina, ferrierite, metal aluminumsilicophosphates,
laumontite, cancrinite, offretite, the hydrogen form of stillbite, the
magnesium or calcium form of mordenite, and the magnesium or calcium form
of partheite, each of which may be used alone or in combination. Many
natural zeolites, such as ferrierite, that have an initially reduced pore
size can be converted to forms suitable for olefin skeletal isomerization
by removing associated alkali metals or alkaline earth metals by ammonium
ion exchange and calcination to produce a substantial hydrogen form. The
isomerization catalyst 62 may also include one or more modifiers, such as
those selected from the group of lanthanum, cerium, praseodymium,
neodymium, samarium, gadolinium, terbium, and mixtures thereof

[0032] The isomerization reaction occurs when hydrocarbons pass through
the isomerization catalyst 62 at isomerization conditions. Isomerization
conditions include a temperature of about 150° C. to about
420° C. and a pressure of about 1,720 kPa absolute (250 psia) to
about 4,720 kPa absolute (700 psia). In another embodiment, the
isomerization conditions include a temperature of about 300° C. to
about 360° C. and a pressure of about 2,400 kPa absolute (350
psia) to about 3,800 kPa absolute (550 psia). Other operating conditions
for the first isomerization reaction zone 60 can also be used.

[0033] The hydrocarbons with the branched paraffins in the isomerization
effluent 64 are processed through one or more separation steps to obtain
a hydrocarbon stream useful as a fuel, and the separation steps vary in
different embodiments. The isomerization effluent 64 includes both a
liquid component and a gaseous component, various portions of which can
be recycled, so multiple separation steps may be employed. For example,
in some embodiments the isomerization effluent 64 is separated in an
isomerization effluent separator 66 positioned downstream from the first
isomerization reaction zone 60. Hydrogen exits the isomerization effluent
separator 66 in an isomerization effluent separator overhead stream 68,
and the liquid portion exits in an isomerization effluent separator
bottoms stream 70. The isomerization effluent separator overhead stream
68 is fed to the enhanced hot separator 52 in some embodiments, so the
gaseous portions are combined with the gases in the enhanced hot
separator overhead stream 54. In other embodiments (not shown), the
isomerization effluent separator overhead stream 68 bypasses the enhanced
hot separator 52 and is eventually used as recycled hydrogen or processed
in other ways.

[0034] Suitable operating conditions of the isomerization effluent
separator 66 include, for example, a temperature of about 280° C.
to about 360° C. and a pressure of about 4,100 kPa absolute (600
psia), but other operating conditions are also possible. If there is a
low concentration of carbon oxides, or the carbon oxides are removed, the
hydrogen may be directly recycled and re-used in the process. Hydrogen is
a reactant in the deoxygenation reaction zone 40 and the first
isomerization reaction zone 60, and different renewable feedstocks 10
will consume different amounts of hydrogen. Additional hydrogen can be
added for feeds that consume more hydrogen. Furthermore, at least a
portion of the isomerization effluent separator bottoms stream 70 can be
recycled to the first isomerization reaction zone 60 (not shown) to
increase the degree of isomerization, to aid in temperature control, or
for other purposes.

[0035] The remainder of the isomerization effluent separator bottoms
stream 70 still has liquid and gaseous components and can be cooled by
various techniques, such as air cooling or water cooling. The liquid
portion of the isomerization effluent separator bottoms stream 70 is
hydrocarbons, including the branched paraffins, as well as some
n-paraffins that were not isomerized into branched paraffins. After
cooling, the isomerization effluent separator bottoms stream 70 is passed
to a cold separator 72 where the liquid component is separated from the
gaseous component. The hot separator overhead stream 48 and the enhanced
hot separator overhead stream 54 are also fed to the cold separator 72,
and can be combined with the isomerization effluent separator bottoms
stream 70 upstream from the cold separator 72. Suitable operating
conditions of the cold separator 72 include, for example, a temperature
of about 40° C. to about 60° C. (about 100° F. to
about 140° F.) and a pressure of about 3,800 kPa absolute to about
5,300 kPa absolute (about 550 to about 770 psia), but other operating
conditions are also possible. A water byproduct stream is also separated
in the cold separator 72 (not shown). A cold separator overhead stream 74
and a cold separator bottoms stream 76 exit the cold separator 72.

[0036] The cold separator overhead stream 74, or the gaseous components
separated in the cold separator 72, is mostly hydrogen and the carbon
dioxide from the decarboxylation reaction. Other components such as CO,
propane, and hydrogen sulfide or other sulfur containing components may
be present as well. Water, CO, and CO2 can negatively impact the
catalyst performance in the first isomerization reaction zone 60. It is
desirable to recycle the hydrogen, but if the CO2 and other
components are not removed, their concentrations can build up and
negatively affect the operation of the first isomerization reaction zone
60. A recovery gas cleaner 78 can be used to increase the purity of the
cold separator overhead stream 74. The carbon dioxide can be removed from
the hydrogen by several different processes, including but not limited to
absorption with an amine, reaction with a hot carbonate solution,
pressure swing absorption, etc. If desired, essentially pure carbon
dioxide can be recovered by regenerating the spent absorption media. A
sulfur containing component, such as hydrogen sulfide, may also be
present. The sulfur containing component may be used to help control the
relative amounts of the decarboxylation reaction and the hydrogenation
reaction in the deoxygenation reaction zone 40. The amount of sulfur is
generally controlled, so the sulfur is also removed before the hydrogen
is recycled. Various methods can be used, such as absorption with an
amine or a caustic wash, and the carbon dioxide and sulfur containing
components (as well as other components) are removed in a single
separation step in some embodiments.

[0037] A recycle hydrogen stream 80 exits the recovery gas cleaner 78
after the impurities have been removed. A recycle hydrogen compressor 82
urges the hydrogen back into the process. As discussed above, the recycle
hydrogen stream 80 may be fed into the renewable feedstock feed stream
18, but the recycle hydrogen stream 80 could be routed into the process
in other locations as well, such as routed directly into the reactors of
the deoxygenation reaction zone 40 or the first isomerization reaction
zone 60. The recycle hydrogen stream 80 supplies the hydrogen for the
guard bed 26 and the deoxygenation reaction zone 40, as discussed above.

[0038] The cold separator bottoms stream 76, or the liquid component
separated in the cold separator 72, contains the liquid hydrocarbons with
the branched paraffins useful as jet fuel and/or diesel fuel, as well as
smaller amounts of naphtha, liquid propane gas (LPG), and other
hydrocarbons. The cold separator bottoms stream 76 may be recovered as
diesel boiling range fuel or it may be further purified in a
fractionation zone 84 that fractionates the various components of the
cold separator bottoms stream. In one embodiment, the fractionation zone
84 includes a product stripper 86 or a product fractionator (not shown)
that can be operated, for example, with a vapor temperature of from about
20° C. to about 200° C. and a pressure from about 0 kPa (0
psia) to about 1,380 kPa absolute (200 psia) at the overhead of the
product stripper 86. In alternate embodiments, the fractionation zone 84
includes a plurality of fractionators and/or separators to divide the
cold separator bottoms stream 76 into various fractions. The
fractionation zone 84 separates the cold separator bottoms stream 76 into
a fractionation zone overhead stream 88, a naphtha product that exits the
fractionation zone 84 at a naphtha outlet 92, and a fractionation zone
bottoms stream 94. The naphtha outlet 92 is split into a naphtha fraction
90 that is collected as a product, and a naphtha reisomerization stream
93.

[0039] The fractionation zone overhead stream 88 includes LPG and lighter
hydrocarbons, such as ethane or methane, and it may include butanes. The
fractionation zone overhead stream 88 can be further fractionated and
sold as a product, used as a fuel gas, or used in other processes such as
the feed to a hydrogen production facility, a co-feed to a reforming
process, or a fuel blending component. The fractionation zone bottoms
stream 94 can be used a diesel range fuel or further fractionated and
used as a jet fuel. The naphtha fraction 90 includes hydrocarbons with
about 5 to 8 carbon atoms, and boils from about 20° C. to about
150° C., where the hydrocarbons are primarily a mixture of
n-paraffins and branched paraffins. In some embodiments, the naphtha is
lightly isomerized after making one pass through an isomerization reactor
58, so it includes relatively few branched paraffins. The naphtha
fraction 90 can be used as a component in gasoline, but it has an octane
value of about 60 to about 70 after a single pass through the
isomerization reactor 58, so a higher octane value would increase the
value of the naphtha fraction 90 for use in gasoline. Most gasoline sold
commercially has an octane value of about 85 to about 95. The octane
value can be increased by converting n-paraffins into branched paraffins.

[0040] In an exemplary embodiment, some of the naphtha product from the
naphtha outlet 92 is further isomerized to convert n-paraffins into
branched paraffins by routing the naphtha reisomerization stream 93 back
to the first isomerization reaction zone 60. Some of the naphtha product
is removed from the process in a naphtha fraction 90 to prevent the
naphtha from building up in the system. The isomerization catalyst 62 in
the first isomerization reaction zone 60 will crack some of the
hydrocarbons in the naphtha into smaller molecules, which decreases the
yield of the final naphtha fraction 90. However, cracking of the
hydrocarbons in the naphtha is minimized by reducing the contact time
with the isomerization catalyst 62 in the first isomerization reaction
zone 60. The naphtha reisomerization stream 93 may be added to the first
isomerization reaction zone 60 by coupling the naphtha outlet 92 to a
side inlet 96 of an isomerization reactor 58 in the first isomerization
reaction zone 60, where the side inlet 96 is positioned with some of the
catalyst bed upstream from the side inlet 96 and some of the catalyst bed
downstream from the side inlet 96. The position of the side inlet 96 can
be adjusted to optimize the degree of isomerization of the naphtha with
the degree of cracking, and in some embodiments the naphtha
reisomerization stream 93 is coupled to the inlet of the isomerization
reactor 58 and contacted with the entire isomerization catalyst bed. A
side inlet 96 configured so the naphtha bypasses some of the
isomerization catalyst 62 also minimizes any dilution effect by the
naphtha on the isomerization of the hydrocarbons with n-paraffins in the
enhanced hot separator bottoms stream 56.

[0041] Reference is now made to the exemplary embodiment illustrated in
FIG. 2, which begins with the cold separator bottoms stream 76. In this
embodiment, the fractionation zone 84 includes a product stripper 86 with
a fractionation zone overhead stream 88 and a fractionation zone bottoms
stream 94. The fractionation zone overhead stream 88 is fed into a light
gas separator 98. A lean gas stream 100 exits the light gas separator as
a gas, and a light gas separator bottoms stream 102 exits as a liquid.
The light gas separator bottoms stream 102 from the light gas separator
98 includes the LPG 104 and the hydrocarbons in the naphtha fraction 118.
The LPG 104 and hydrocarbons in the naphtha fraction 118 (prior to
isomerization) are further separated in a debutanizer 106 that produces
the LPG 104 as an overhead stream and the naphtha reisomerization stream
93 as a bottom stream. The naphtha reisomerization stream 93 exits the
debutanizer 106 at the naphtha outlet 92. The debutanizer 106 can be
operated, for example, at a vapor temperature of about 20° C. to
about 200° C. and a pressure from about 0 to about 2,760 kPa
absolute (0 to 400 psia) at the debutanizer overhead, but other
conditions are also possible.

[0042] The naphtha outlet 92 from the debutanizer 106 is coupled to an
isomerization reactor 114 in a second isomerization reaction zone 110 to
further isomerize the paraffins in the naphtha fraction 118. In some
embodiments, the second isomerization reaction zone 110 includes an
isomerization catalyst 116 and operates at isomerization conditions. The
second isomerization reaction zone 110 can be operated to match the feed
from the naphtha outlet 92, and a suitable isomerization catalyst 116 and
isomerization conditions can be used. In an exemplary embodiment, the
isomerization catalyst 116 includes about 0.01 to about 3 weight percent
of a metal on an inorganic oxide carrier, and includes a halide as a
promoter. Suitable inorganic oxide carriers include alumina, silica,
zirconia, magnesia, thoria, and combinations thereof, but other carriers
can also be used. Suitable metals include Ruthenium, Rhodium, Palladium,
Osmium, Iridium, and Platinum, and the weight percent is determined based
on the weight of the metal, regardless of the form of the metal on the
carrier. The halide promoter is present at about 0.1 to about 10 weight
percent, and includes chlorides or other halides. Suitable isomerization
conditions include a temperature from about 120° C. to about
200° C. (about 250° F. to about 400° F.), and
pressures from about 2,400 kPa to about 3,800 kPa (about 350 PSIG to
about 550 PSIG).

[0043] The second isomerization reaction zone 110 can be used in place of,
or in conjunction with, a naphtha recycle through the first isomerization
reaction zone. The naphtha reisomerization stream 93 is the primary feed
to the second isomerization reaction zone 110, so the size of the
isomerization reactor 114 and catalyst bed, the quantity of isomerization
catalyst 116 used, and the isomerization conditions can be optimized for
the naphtha reisomerization stream 93. A second isomerization reaction
zone hydrogen line 112 can be used to introduce hydrogen for the
isomerization reaction. The naphtha fraction 118 then exits the second
isomerization reaction zone 110 with a higher level of branched paraffins
than the feed to the second isomerization reaction zone 110. An optional
separator (not shown) can be installed downstream from the second
isomerization reaction zone 110 to vent hydrogen and light gases produced
by cracking in the isomerization reactor 114, and the vented hydrogen can
be reused in a similar manner to the hydrogen collected in the hot
separator overhead stream.

[0044] Reference is now made to FIG. 1 again. The exemplary embodiments
described above include many optional processes, or processes that can be
modified or arranged in different manners. In a very simplified form, the
renewable feedstock feed system 12 is coupled to the deoxygenation
reaction zone 40, because the renewable feedstock 10 flows to the
deoxygenation reaction zone 40. The deoxygenation reaction zone 40 is
likewise coupled to the first isomerization reaction zone 60, which is
coupled to the fractionation zone 84, even though several vessels or
processes are positioned between the different zones. The naphtha is
recovered from the fractionation zone 84 and re-isomerized to increase
the concentration of branched paraffins. Several vessels and steps are
used to recover and reuse hydrogen throughout the manufacturing process.

[0045] It should be appreciated that the embodiment or embodiments
illustrated are only examples, and are not intended to limit the scope,
applicability, or configuration of the application in any way. Rather,
the foregoing detailed description will provide those skilled in the art
with a convenient road map for implementing one or more embodiments, it
being understood that various changes may be made in the function and
arrangement of elements described without departing from the scope as set
forth in the appended claims.